2016 G面试题#2 不构造树的情况下验证先序遍历

 def isValidTree(POTra):
     """
     POTra :param list:
     :return:
     """

     if not POTra:
         return True

     while len(POTra) > 1:
         index = []
         n = len(POTra)
         for i in range(0, n-2):
             if POTra[i] != '#' and POTra[i+1] == '#' and POTra[i+2] == '#':
                 POTra[i] = '#'
                 index.append(i+1)
                 index.append(i+2)
             else:
                 continue
         removeset = set(index)
         POTra = [v for i, v in enumerate(POTra) if i not in removeset]
         #print(POTra)
         if len(POTra) == n:
             break

     if POTra == ['#']:
         return True
     else:
         return False

Keys: 在一个list中根据index可以同时去掉多个element, see L21